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Kubernetes

What's k8s​

Resource boundaries in different deployment era:

  • Traditional - No boundary
  • Virtualized - Isolated resource and security
  • Container - Bin + app

Facilitate Canary deployments

minikube​

minikube provisions and manages local Kubernetes clusters optimized for development workflows.

MiniKube vs MicroK8s

Why k8s?​

  • Service discovery and load balancing
  • Storage orchestration
  • Automated rollouts and rollbacks
  • Automatic bin packing
  • Self-healing
  • Secret and configuration management

k8s components​

Control Plane Components​

  • k8s cluster = a set of worker machines(nodes)
  • pods : smallest deployable units
  • kube-apiserver: Front end of control plane
  • etcd: distributed data store for cluster data.
  • kube-scheduler: allocate newly created pods to an available node.
  • kube-controller-manager: Node, Replication, Endpoints, Service Account & Token controller.
  • cloud-controller-manager: Node, Route, Service controller dependencies.

Node components​

  • kubelet: manages docker to conform PodSpecs
  • kube-proxy: k8s service implementation.
  • Container runtime: Docker

Addons​

  • DNS: For service and pods
  • Dashboard; UI
  • Container Resource Monitoring
  • Cluster-level Logging

K8s diagrams

k3s vs minikube vs kind

The Kubernetes API​

Open API API object needs to handle buffer, xml or json?

Google developed protobuf before.

protobuf like design

Kubernetes Objects - "record of intent"​

Kubernetes objects are persistent entities in the Kubernetes system.

  • Object Spec: describe the desired state
  • Status: current state of the object, managed by k8s control plane.

Management techniques​

  • Imperative commands: kubectl
  • Imperative object config: .yaml file
  • Declarative object config: directory of files.

Troubleshooting: k8s error image pullbackoff

Object Names and IDs​

  • Names: /api/v1/pods/some-name

  • IDs: UUID to track historical occurrences.

Namespaces​

Virtual cluster

kubectl get namespace

Namespaces and DNS:

When you create a Service, it creates a corresponding DNS entry.

Labels and selectors​

Labels = Identifying key/values

selectors: filtering via label.

  • equality-based : =, ==, !=

  • set-based : in,notin and exists

Annotations​

arbitrary non-identifying metadata to objects.

Field Selectors​

kubectl get pods --field-selector status.phase=Running

Cluster architecture​

Nodes​

Components: kubelet,

a container runtime, and the kube-proxy

Adding nodes:

  • kubelet can self-register

  • user manually add

Pod​

Pod is the smallest deployable unit, one or more containers with shared resources and network. It can contain init containers and ephemeral containers for debugging.

Workload resource manage pods: Deployment or Job. track state StatefulSet